Area contact truss strut joint

ABSTRACT

A strut joint of a truss features a contact trough on an inner chord face being in an area contact with a rotationally symmetric strut end surface having a contact radius of at least half a strut height. The rotation axis of the strut end surface and the trough is substantially perpendicular to the struts protrusion direction and the chord&#39;s protrusion direction. The area contact provides for snug contact irrespective deviations from a predetermined strut joint angle between strut end and chord. An optional interposing structure may extend the area contact in between two opposite strut end surfaces of a single strut joint.

CROSS REFERENCE

The present Application claims priority from Provisional Application ofthe same title and inventor, filed Mar. 08, 2005, Ser. No. 60/659,988,which is hereby incorporated by reference.

FIELD OF INVENTION

The present invention relates to trusses having chords and struts. Moreparticular, the present invention relates to trusses having strut jointswith rotationally symmetric area contact between strut and chord.

BACKGROUND OF INVENTION

The load carrying capacity of a truss greatly depends on the rigidity ofthe strut joints where web struts of a truss are combined with thechords. A prior art truss 10 as shown in FIG. 1 includes top and bottomchords 11 combined along their respective inner chord faces 111 via anumber of web struts 12. The ends of the web struts 12 define at theirattachment locations on the inner chord faces 111 together with thechords 11 the strut joints 13. The web struts 12 are attached to thechords 111 in varying strut joint angles SA with respect to the struttilt axes TA. To keep the buckling resistance to a maximum, the truss 10is preferably a planar structure symmetric with respect to a symmetryplane SP. The strut tilt axes TA are consequently preferablyperpendicular to the symmetry plane SP.

Strut joints 13 are also preferably symmetric with respect to symmetryplane SP. Prior art strut joints 13 of prior art FIGS. 2, 3 have one oretwo tapered end surfaces 121. In cases of single tapered end surfaces121 as in FIG. 2, there exists a high likelihood of line contact LCbetween end surfaces 121 and inner chord faces 111, which may resultfrom limited truss 10 assembly precision and/or assembly deviations frompredetermined strut joint angles SA.

In case of two tapered end surfaces 121, there may be an additionalrounding between the two tapered end surfaces 121 as shown in FIG. 3.Such prior art strut end configuration is designed to make the strutjoints 13 independent of above mentioned deviations of predeterminedstrut joint angle SA and to provide a standardized strut endconfiguration. Even rounded strut end surfaces 121 provide only linecontact LC with the inner chord faces 111. Due the small tip radius thatis substantially smaller than the strut's height half HH, indentationsof the strut tip radii into the contacting chord face 111 may even beworth than in a configuration of prior art FIG. 2.

Exclusive Line contact LC, especially between the strut end surfaces 121and the inner chord faces 111 has very little compressive loadtransmission capability resulting in a deformation of both inner chordfaces 111 and chord end surfaces 121. As a result, the joint plates 14commonly laterally and oppositely nailed or screwed onto the chords 11and the struts 12 at the strut joints 13, end up as load transmittingelements, whereby the nail or screw connections become additionallyshear stressed. This may eventually reduce the overall stiffness andload carrying capacity of the truss 10. Therefore, there exists a needfor strut joints with area contact between the strut ends and the chordthat is highly independent of strut angle offset. The present inventionaddresses this need.

SUMMARY

A well known truss used in architectural construction includes a numberof web struts combined with top and bottom chords in several strutjoints along inner chord faces. The struts are oriented with varyingstrut joint angles with respect to the respective chord. In the presentinvention, area contact is established in the strut joints betweenrotationally symmetric strut end surfaces being in a snug contact withcorrespondingly shaped contact troughs provided at the inner chordsurfaces. Strut ends and troughs may have a standardized configurationthat complies with a range of the strut joint angles. The troughs may becut into the chord whereby the chord grain is interrupted and/or may bepressed into the inner chord faces whereby the chord grain is compressbut remains substantially continuous.

In alternate embodiments, an interposing structure may be added to thestrut joint. It may be placed between the strut ends and the chords toeither partially extend the trough surface for an enlarged area contactwith the strut end. Alternately, the interposing structure may provideentire trough surface whereby a reduction of the chord's cross sectiondue to the trough is circumvented while the advantageous area contact ismaintained. The interposing structure may rest on the inner chord face.Positioning of the interposing structure may be provided by apositioning groove fabricated into the inner chord face and/or acorresponding positioning feature of the interposing structure. Theinterposing structure may be part of a prefabricated assembly includinglateral joint plates. The preassembly may clamp along the chords in afriction contact and be aligned with a positioning label on the chordsindicating the predetermined position of the strut joint. As a favorableresult of the area contact, overall truss stiffness and load carryingcapacity may be improved without increasing dimensions of struts and/orchords

A chord fabrication system may include a trough fabrication devicepositioned along a chord fabrication path to fabricate the troughs atpredetermined positions along the chords. In addition or alternately, aposition defining device may fabricate the positioning grooves and/orpositioning labels into the chords.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of a representative prior art truss.

FIG. 2 is the perspective view of a first representative prior art strutjoint with the removed foreground plate.

FIG. 3 is the perspective view of a second representative prior artstrut joint with removed foreground plate.

FIG. 4 is the perspective view of a first embodiment of the presentinvention with removed foreground plate and interrupted chord grain.

FIG. 5 is the strut joint of FIG. 4 with continuous chord grain.

FIG. 6 is a second embodiment of the present invention including aninterposing structure placed between two adjacent strut end surfaces ofa strut joint.

FIG. 7 is a third embodiment of the present invention including aninterposing structure placed between the strut end surfaces and thechord.

FIG. 8 schematically depicts a chord fabrication system for fabricatingchords in accordance with the present invention.

DETAILED DESCRIPTION

The present invention introduces improved strut joints 23 of FIGS. 4-7with area contact at least in an interface between a chord trough 212and a strut end surface 221 between the modified struts 22 and innerchord faces 211 of modified chords 21 as depicted in FIGS. 4, 5. Areacontact may also extend directly between adjacent modified chord endsurfaces 221 of a modified strut joint 23 as illustrated in FIGS. 6, 7.

Primary area contact is provided between at least rotationally symmetricstrut end surfaces 221 and corresponding at least rotationally symmetriccontact troughs 212. The contact troughs 212 are rotationally symmetricwith respect to a trough axis 212A that is substantially perpendicularto the truss symmetry plane SP, a chord protrusion direction CD, a strutprotrusion direction PD and parallel to the strut tilt axes TA. As aresult, the struts 22 may be combined with the inner chord faces 211 ina primary area contact irrespective their strut joint angle SA.

Contact troughs 212 and strut end surfaces 221 are at least rotationallysymmetric but preferably cylindrical and may have a contact radius CRthat is at a maximum for a predetermined range of strut joint angle SA,within which the struts 22 may be assembled while exclusivelymaintaining area contact between strut end surfaces 221 and theirrespective contact trough 212. More particular, a strut end surface 221may have an end surface angle EA. The end surface angle EA may have asymmetric axis ESA, which may be in an angle with respect to itsrespective web strut's 12 protrusion direction PD. In such a case theend surface angle EA and the end surface symmetry axis ESA may beselected such that the respective strut end surface 221 extends at leastup to a peripheral trough edge TEP and a strut contact line SCL betweentwo oppositely contacting strut end surfaces 221. More particularly, twoadjacent troughs 212 of a strut joint 23 including two struts 22 mayshare a single central trough edge TEC in case of which the strutcontact line SCL may substantially coincide with the central trough edgeTEC.

In the case of the end surface symmetric axis ESA being collinear withthe strut protrusion direction PD, the end surface angle EA may beselected for a given strut joint angle SA and a trough angle TAN of therespective truss joint 23 such that the respective strut end surface 221extends at least up to a peripheral trough edge TEP and the strutcontact line SCL. More particular, all struts 22 of a truss may have asubstantially equal end surface angle EA such that for the strut jointangle SA being in a range between a maximum and a minimum at a number oftruss joints 23, each of the end surfaces 221 of the respective trussextend et least up their respective peripheral trough edge TEP and theirrespective strut contact line SCL. In this preferred case, fabricationof troughs 212 and strut end surfaces 221 may be accomplished withrespective standards for individual strut 22 lengths and at varyingtrough 212 locations along the inner chord face 211.

The end surface angle EA may be up to 180 degrees and the contact radiusCR at least half a height SH of a strut side face 229 substantiallyperpendicular to the rotation axis of the end surface 221. Having thecontact radius CR at least half the height SH provides for a maximumarea in the interface between trough 212 and respective end surface 221,which in turn assists in reducing contact pressure and deformation inthe strut joint 23 resulting in an increased overall stiffness of atruss having strut joints 23.

In case of the chord 21 being made of wood as shown in FIG. 4, contacttroughs 212 may be fabricated with well known cutting techniquesresulting in interrupted chord grains 213 in the vicinity of the trough212. Alternately and also in case of a wooden chord 21 as shown in FIG.5, contact troughs 212 may be fabricated with non-cutting fabricationtechniques resulting in substantially continuous chord grains 213 in thevicinity of the troughs 212. Continuous chord grains 213 may improve thechord's 21 strength and/or splicing tendency in the vicinity of thetrough 212 as may be well appreciated by anyone skilled in the art. Anon-cutting fabrication technique may be a pressing technique as may bewell appreciated by anyone skilled in the art.

In the first embodiment of the invention described under FIGS. 4, 5,line contact exists along the strut contact line SCL directly betweenthe strut end surfaces 221. As strut joint angles SA become smaller, thestrut contact line SCL may become increasingly loaded. In a second andthird embodiment of the invention depicted in FIGS. 6, 7, a secondaryarea contact is provided directly between the adjacent strut endsurfaces of a single strut joint 23. The secondary area contact is abovethe level of the inner chord faces 211 by an interposing structure 24placed at least between the two adjacent strut end surfaces 221 and ontop of the inner chord face 211 adjacent a through 212. The interposingstructure 24 rests with a flat contact face 243 on the inner chord face211. The interposing structure 24 may be positioned on the inner chordface 211 via a protruding positioning feature 241 fitting in a chordgroove 214. The interposing structure 24 may have plate connect features244 for attaching and positioning the joint plates 14 with theinterposing structure 24.

In the second embodiment of FIG. 6, the interposing structure 24 has atleast one but preferably two contact surfaces 242 corresponding to andextending from the contact troughs 212 while the interposing structure24 is in assembled position on the inner chord face 211. In the thirdembodiment of FIG. 7, the interposing structure 24 may provide primaryand secondary area contact with fully interposing surfaces 242. Thestrut end surfaces 221 contact solely the interposing structure 24 andthe inner chord faces 211 may feature only positioning grooves 214.

The interposing structure 24 may be combined with two opposing jointplates 14 of a strut joint 23 in a preassembly that may providesufficient stiffness for a friction based damping onto the chords 21.The use of such preassembly may ease the truss fabrication process. Thefriction based damping and positioning of the preassembly may eliminatethe need for a positioning groove 214 such that the inner chord face 211may remain continuous. A positioning label 26 may be substituted for thepositioning groove. A reference mark may be provided at the preassemblyto position the preassembly with respect to the previously fabricatedpositioning label 25. The positioning label 25 may give also informationabout a required length of the strut 22 to be assembled at therespective strut joint 23.

A chord fabrication system 300 schematically depicted in FIG. 8, mayfabricate chords 21 from chord raw material 2 along a fabrication path302 as is well known in the art. Such chord fabrication system 300 mayinclude a fabrication device 301 for fabricating the contact troughs 212and/or positioning grooves 214 and/or positioning labels 25 atpredetermined positions along the chord 21 and in accordance with theteachings above.

Accordingly, the scope of the invention described in the Figures and theSpecification above is set forth by the following claims and their legalequivalent:

1. A strut having a rotationally symmetric end surface, saidrotationally symmetric end surface having a contact radius of at leasthalf of a height of a strut side face and having an end surface angle ofup 180 degrees, wherein a rotation axis of said end surface issubstantially perpendicular to said strut side face.
 2. The strut ofclaim 1, wherein said end surface is in an area contact with a trough onan inner face of a chord, said end surface and said trough being part ofa strut joint, and wherein said strut is in a strut joint angle to saidchord.
 3. The strut of claim 2, wherein said strut contacts a second ofsaid strut in a strut contact line.
 4. The strut of claim 3, whereinsaid end surface angle is selected such that said strut contact line iswithin said end surface.
 5. The strut of claim 3, wherein a number ofsaid strut joint are part of a truss and wherein a number of said strutof said truss have said end surface angle substantially equal andselected in conjunction with a maximum and a minimum of said strut jointangle and selected in conjunction with a trough angle such that saidnumber of said end surfaces extend at least up to a peripheral edge of arespective of said trough and a respective of said strut contact line.6. The strut of claim 1, wherein said end surface is in contact with aninterposing trough surface of an interposing structure.
 7. The strut ofclaim 1 being made of wood.
 8. A chord comprising a rotationallysymmetric contact trough on a face of said chord, said contact troughbeing rotationally symmetric with respect to a trough axis, said troughaxis being substantially perpendicular to a protrusion direction of saidchord.
 9. The chord of claim 8 being made of wood and wherein said chordhas interrupted chord grains in a vicinity of said contact trough. 10.The chord of claim 8 being made-of wood and wherein said chord hassubstantially continuous chord grains in a vicinity of said contacttrough.
 11. The chord of claim 8, wherein said trough is in an areacontact with an end surface of a strut, said end surface and said troughbeing part of a strut joint, and wherein said strut is in a strut jointangle to said chord.
 12. The chord of claim 8, further comprising aninterposing structure adjacent said contact trough and on top of saidchord face, said interposing structure having a contact surfacecorresponding to and extending from said contact trough.
 13. The chordof claim 8, wherein said contact trough is provided by an interposingstructure placed on said chord face.
 14. A truss having a strut jointcomprising a strut having a rotationally symmetric end surface in anarea contact with a rotationally symmetric trough on an inner chordface, said end surface and said trough having a rotation axissubstantially perpendicular to a symmetry plane of said truss, andwherein said strut is in a strut joint angle to said chord.
 15. Thetruss of claim 14, wherein said end surface has a contact radius of atleast half of a height of strut side face and an end surface angle of up180 degrees.
 16. The truss of claim 14, wherein said strut contacts asecond of said strut in a strut contact line within said strut joint.17. The truss of claim 16, wherein said end surface angle is selectedsuch that said strut contact line is within said end surface.
 18. Thetruss of claim 16, wherein a number of said strut joint have said endsurface angle substantially equal and selected in conjunction with amaximum and a minimum of said strut joint angle and selected inconjunction with a trough angle such that said number of said endsurfaces extend at least up to a peripheral edge of a respective of saidtrough and a respective of said strut contact line.
 19. The truss ofclaim 14, wherein said chord is made of wood and wherein said chord hasinterrupted chord grains in a vicinity of said contact trough.
 20. Thetruss of claim 14, wherein said chord is made of wood and wherein saidchord has substantially continuous chord grains in a vicinity of saidcontact trough.
 21. The truss of claim 14, further comprising aninterposing structure adjacent said contact trough and on top of saidchord face, said interposing structure having a contact surfacecorresponding to and extending from said through, and wherein saidcontact surface is in an area contact with said end surface.
 22. Thetruss of claim 14, wherein said trough is provided by an interposingstructure placed on said inner chord face.